1. Field of the Invention
The present invention relates to a magnetic head for reproducing magnetically recorded information, and more particularly, to a magnetic head, utilizing magnetic impedance effect, to reproduce digital information which is magnetically recorded.
2. Brief Description of the Related Art
According to high density integration of recent digital techniques, which is progressed in the external storing device of a computer, such as hard disk devices or digital compact cassette tape recorders, the decrease of S/N ratio due to a decrease of the track width or decrease of speed is caused in a conventional induction-type magnetic head, and therefore a magnetic resistance element (hereinafter, referred to MR element) is utilized as a reproducing head.
The MR element, which is free from speed dependency on the magnetic recording medium, is suitable for deriving the output at low speed, however it has a resistance change of as low as several percent. It is therefore desired to develop elements that are further improved in sensitivity in order to comply with future high density designs.
In this connection, a system of this type that is particularly remarkable has been disclosed in recent years, for example, in Japanese laid-open patent publication No. 7-181239/1995 which describes a magnetically detectable head utilizing magnetic impedance effect (hereinafter, referred to "MI element").
The "magnetic impedance effect" referred herein relates to a phenomenon that, a high frequency current of a MHz (mega Hertz) band is caused to flow through a magnetic material. The impedance of the material changes according to the external magnetic field, and accordingly the amplitude of the terminal voltage of the magnetic material can vary by as high as tens % within a minute magnetic field of as low as several gauss. It is expected, when such a MI element is applied to a magnetic head, an excellent performance which has never seen in the past would be obtained.
However, in the case that a MI element is simply utilized for a magnetic head, there would be caused the hereinafter described problems.
Since a MI element has normally a property that it is sensitive in the longitudinal direction of the element, it is necessary to approach or engage with one end of the element with the recording medium to hence draw the magnetic flux to the interior of the element. For this purpose, for example, as shown in FIG. 17, if a MI element 102 is positioned so as to extend perpendicular to magnetic medium 100, the magnetic flux concentrates at the end tip of MI element 102, and rapidly decreases as deviated from the medium 100. Thus, the region having an increased impedance change concentrates at the end tip of MI element 102, and hence the sufficient sensitivity of MI element 102 as a whole cannot be attained. Alternatively, although, by decreasing the length of MI element 102, the efficiency of impedance change might be increased, yet the increase of demagnetizing field in the direction of detection, that is, in the longitudinal direction and the lowering of impedance are caused, thereby with still no improvement in sensitivity being achieved.